The **difference** of a number and $6$ is $13$. What is the number?

Let $n$ be the number. "The difference of a number and 6" translates to $n - 6$. Setting this equal to $13$: $n - 6 = 13 \Rightarrow n = 19$. Check: $19 - 6 = 13$ ✓. - Trap A ($7$) subtracts in the wrong direction ($13 - 6$). - Trap B ($9$) gives $13 + 6$ at the wrong stage of the arithmetic. - Trap D ($20$) is close to the right answer but off by one — common if the student writes $n - 6 = 14$.